Identification Code or EPA I.D. Number: The unique code assigned
to each generator, transporter, and treatment, storage, or disposal facility
by regulating agencies to facilitate identification and tracking of chemicals
or hazardous waste.

Imhoff Cone: A clear, cone-shaped container used to measure the
volume of settleable solids in a specific volume of water.

Immediately Dangerous to Life and Health (IDLH): The maximum level
to which a healthy individual can be exposed to a chemical for 30 minutes
and escape without suffering irreversible health effects or impairing
symptoms. Used as a "level of concern." (See: level
of concern.)

Imminent Hazard: One that would likely result in unreasonable
adverse effects on humans or the environment or risk unreasonable hazard
to an endangered species during the time required for a pesticide registration
cancellation proceeding.

Imminent Threat: A high probability that exposure is occurring.

Immiscibility: The inability of two or more substances or liquids
to readily dissolve into one another, such as soil and water. Immiscibility
The inability of two or more substances or liquids to readily dissolve
into one another, such as soil and water.

Impermeable: Not easily penetrated. The property of a material
or soil that does not allow, or allows only with great difficulty, the
movement or passage of water.

Imports: Municipal solid waste and recyclables that have been
transported to a state or locality for processing or final disposition
(but that did not originate in that state or locality).

Impoundment: A body of water or sludge confined by a dam, dike,
floodgate, or other barrier.

In Situ: In its original place; unmoved unexcavated; remaining
at the site or in the subsurface.

In-Line Filtration: Pre-treattment method in which chemicals are
mixed by the flowing water; commonly used in pressure filtration installations.
Eliminates need for flocculation and sedimentation.

In-Situ Flushing: Introduction of large volumes of water, at times
supplemented with cleaning compounds, into soil, waste, or ground water
to flush hazardous contaminants from a site.

In-Situ Stripping: Treatment system that removes or "strips"
volatile organic compounds from contaminated ground or surface water by
forcing an airstream through the water and causing the compounds to evaporate.

In-Situ Vitrification: Technology that treats contaminated soil
in place at extremely high temperatures, at or more than 3000 degrees
Fahrenheit.

In Vitro: Testing or action outside an organism (e.g. inside a
test tube or culture dish.)

In Vivo: Testing or action inside an organism.

Incident Command Post: A facility located at a safe distance from
an emergency site, where the incident commander, key staff, and technical
representatives can make decisions and deploy emergency manpower and equipment.

Incident Command System (ICS): The organizational arrangement
wherein one person, normally the Fire Chief of the impacted district,
is in charge of an integrated, comprehensive emergency response organization
and the emergency incident site, backed by an Emergency Operations Center
staff with resources, information, and advice.

Incineration: A treatment technology involving destruction of
waste by controlled burning at high temperatures; e.g., burning sludge
to remove the water and reduce the remaining residues to a safe, non-burnable
ash that can be disposed of safely on land, in some waters, or in underground
locations.

Incineration at Sea: Disposal of waste by burning at sea on specially-designed
incinerator ships.

Incinerator: A furnace for burning waste under controlled conditions.

Incompatible Waste: A waste unsuitable for mixing with another
waste or material because it may react to form a hazard.

Indemnification: In the pesticide program, legal requirement that
EPA pay certain end-users, dealers, and distributors for the cost of stock
on hand at the time a pesticide registration is suspended.

Indicator: In biology, any biological entity or processes, or
community whose characteristics show the presence of specific environmental
conditions. 2. In chemistry, a substance that shows a visible change,
usually of color, at a desired point in a chemical reaction. 3.A device
that indicates the result of a measurement; e.g. a pressure gauge or a
moveable scale.

Indirect Discharge: Introduction of pollutants from a non-domestic
source into a publicly owned waste-treatment system. Indirect dischargers
can be commercial or industrial facilities whose wastes enter local sewers.

Industrial Sludge: Semi-liquid residue or slurry remaining from
treatment of industrial water and wastewater.

Industrial Source Reduction: Practices that reduce the amount
of any hazardous substance, pollutant, or contaminant entering any waste
stream or otherwise released into the environment. Also reduces the threat
to public health and the environment associated with such releases. Term
includes equipment or technology modifications, substitution of raw materials,
and improvements in housekeeping, maintenance, training or inventory control.

Industrial Waste: Unwanted materials from an industrial operation;
may be liquid, sludge, solid, or hazardous waste.

Inert Ingredient: Pesticide components such as solvents, carriers,
dispersants, and surfactants that are not active against target pests.
Not all inert ingredients are innocuous.

Infiltration: 1. The penetration of water through the ground surface
into sub-surface soil or the penetration of water from the soil into sewer
or other pipes through defective joints, connections, or manhole walls.
2. The technique of applying large volumes of waste water to land to penetrate
the surface and percolate through the underlying soil. (See: percolation.)

Infiltration Gallery: A sub-surface groundwater collection system,
typically shallow in depth, constructed with open-jointed or perforated
pipes that discharge collected water into a watertight chamber from which
the water is pumped to treatment facilities and into the distribution
system. Usually located close to streams or ponds.

Infiltration Rate: The quantity of water that can enter the soil
in a specified time interval.

Inflow: Entry of extraneous rain water into a sewer system from
sources other than infiltration, such as basement drains, manholes, storm
drains, and street washing.

Influent: Water, wastewater, or other liquid flowing into a reservoir,
basin, or treatment plant.

Information Collection Request (ICR): A description of information
to be gathered in connection with rules, proposed rules, surveys, and
guidance documents that contain information-gathering requirements. The
ICR describes what information is needed, why it is needed, how it will
be collected, and how much collecting it will cost. The ICR is submitted
by the EPA to the Office of Management and Budget (OMB) for approval.

Information File: In the Superfund program, a file that contains
accurate, up-to-date documents on a Superfund site. The file is usually
located in a public building (school, library, or city hall) convenient
for local residents.

Insecticide: A pesticide compound specifically used to kill or
prevent the growth of insects.

Inspection and Maintenance (I/M): 1. Activities to ensure that
vehicles' emission controls work properly. 2. Also applies to wastewater
treatment plants and other anti-pollution facilities and processes.

Instream Use: Water use taking place within a stream channel;
e.g., hydro-electric power generation, navigation, water quality improvement,
fish propagation, recreation.

Integrated Exposure Assessment: Cumulative summation (over time)
of the magnitude of exposure to a toxic chemical in all media.

Integrated Pest Management (IPM): A mixture of chemical and other,
non-pesticide, methods to control pests.

Integrated Waste Management: Using a variety of practices to handle
municipal solid waste; can include source reduction, recycling, incineration,
and landfilling.

Interceptor Sewers: Large sewer lines that, in a combined system,
control the flow of sewage to the treatment plant. In a storm, they allow
some of the sewage to flow directly into a receiving stream, thus keeping
it from overflowing onto the streets. Also used in separate systems to
collect the flows from main and trunk sewers and carry them to treatment
points.

Interface: The common boundary between two substances such as
a water and a solid, water and a gas, or two liquids such as water and
oil.

Interfacial Tension: The strength of the film separating two immiscible
fluids (e.g. oil and water) measured in dynes per, or millidynes per centimeter.

Interim (Permit) Status: Period during which treatment, storage
and disposal facilities coming under RCRA in 1980 are temporarily permitted
to operate while awaiting a permanent permit. Permits issued under these
circumstances are usually called "Part A" or "Part B"
permits.

Internal Dose: In exposure assessment, the amount of a substance
penetrating the absorption barriers (e.g. skin, lung tissue, gastrointestinal
tract) of an organism through either physical or biological processes.
(See: absorbed dose)

Interstate Carrier Water Supply: A source of water for drinking
and sanitary use on planes, buses, trains, and ships operating in more
than one state. These sources are federally regulated.

Interstate Commerce Clause: A clause of the U.S. Constitution
which reserves to the federal government the right to regulate the conduct
of business across state lines. Under this clause, for example, the U.S.
Supreme Court has ruled that states may not inequitably restrict the disposal
of out-of-state wastes in their jurisdictions.

Interstate Waters: Waters that flow across or form part of state
or international boundaries; e.g. the Great Lakes, the Mississippi River,
or coastal waters.

Interstitial Monitoring: The continuous surveillance of the space
between the walls of an underground storage tank.

Intrastate Product: Pesticide products once registered by states
for sale and use only in the state. All intrastate products have been
converted to full federal registration or canceled.

Inventory (TSCA): Inventory of chemicals produced pursuant to
Section 8 (b) of the Toxic Substances Control Act.

Inversion: A layer of warm air that prevents the rise of cooling
air and traps pollutants beneath it; can cause an air pollution episode.

Ion: An electrically charged atom or group of atoms.

Ion Exchange Treatment: A common water-softening method often
found on a large scale at water purification plants that remove some organics
and radium by adding calcium oxide or calcium hydroxide to increase the
pH to a level where the metals will precipitate out.

Ionization Chamber: A device that measures the intensity of ionizing
radiation.

Irradiated Food: Food subject to brief radioactivity, usually
gamma rays, to kill insects, bacteria, and mold, and to permit storage
without refrigeration.

Irradiation: Exposure to radiation of wavelengths shorter than
those of visible light (gamma, x-ray, or ultra- violet), for medical purposes,
to sterilize milk or other foodstuffs, or to induce polymerization of
monomers or vulcanization of rubber.

Irreversible Effect: Effect characterized by the inability of
the body to partially or fully repair injury caused by a toxic agent.

Irrigation: Applying water or wastewater to land areas to supply
the water and nutrient needs of plants.

Irrigation Efficiency: The amount of water stored in the crop
root zone compared to the amount of irrigation water applied.

Irrigation Return Flow: Surface and subsurface water which leaves
the field following application of irrigation water.

Irritant: A substance that can cause irritation of the skin, eyes,
or respiratory system. Effects may be acute from a single high level exposure,
or chronic from repeated low-level exposures to such compounds as chlorine,
nitrogen dioxide, and nitric acid.

Isoconcentration: More than one sample point exhibiting the same
isolate concentration.

Isopleth: The line or area represented by an isoconcentration.

Isotope: A variation of an element that has the same atomic number
of protons but a different weight because of the number of neutrons. Various
isotopes of the same element may have different radioactive behaviors,
some are highly unstable..

Isotropy: The condition in which the hydraulic or other properties
of an aquifer are the same in all directions.